The present invention is directed toward semiconductor transistors, and more particularly to lateral bipolar junction transistors (BJTs) with emitter-collector regions.
From the mid to the late 1970's, there was a lot of excitement in the VLSI industry about the prospect of Integrated Injection Logic (I2L). I2L is by far the densest circuit. It uses small sized devices, and requires one PNP per gate for current injection and only one NPN per fan-out. Thus an inverter with FO=3 takes only four transistors. The NPN transistors in an I2L circuit operate in the reverse-active mode. As a result, even with advanced self-aligned vertical Si-based BJT technology, I2L has minimum delays not much below one ns. This speed limitation, together with the rapid progress in complementary metal-oxide semiconductor (CMOS) scaling in the early 1980's, caused the demise of I2L.
Many modern technologies, such as high-speed communications, radar applications, and millimeter wave (mmwave) and THz imaging and sensing, require transistor operation in the hundreds of GHz. Silicon-on-insulator (SOI) complementary metal-oxide-semiconductor (CMOS) allows stacked NFET to use voltage supply higher than the bulk-FET drain junction breakdown voltage. This has allowed SOI-CMOS to be competitive for mmwave output power and efficiency. However, advanced CMOS breakdown is now limited by the gate dielectric breakdown and hot carriers. Therefore, advanced CMOS using a VDD supply of 1V or less limits the generation of power beyond 100 GHz.
SiGe-BJT are also competitive but are currently limited by the number of devices that can be stacked (typically two), because of the use of bulk Si substrates. The maximum collector-to-emitter voltage that can be used in a stacked configuration is limited by the collector-to-substrate breakdown voltage. As a vertical SiGe heterojunction bipolar transistor (HBT) is driven to higher currents, the transistor speed and circuit speed increase. However, once the current exceeds a critical level, base-pushout (Kirk effect) kicks in and the transistor and circuit speeds decrease rapidly as current is increased further.